Tuesday, 7 October 2014

The Planning

I was planning, thinking, imagining the launch and the flight all along the preparations, but with the payload becoming ready, the planning became more specific.

At first, I summed up the circumstances and some expectations I had about the flight. For example, my launch site was fixed to a local company's parking lot, because I would use their helium supplies to fill my balloon. That put pressure on choosing the right day with the right wind conditions, because I couldn't relocate the launch to a better position. Another demand I had was that if possible, the balloon should land somewhere in a field as opposed to a hilly or mountainous terrain covered by trees.

The launch location would be in Roznov pod Radhostem. Basically any eastward trajectory would end up in mountains that are mostly forested. That would be the worst conditions for a successful recovery. Additionally, it would most likely cross the borders and ended up in Slovakia. On the other hand, the westward direction seemed much more suitable. The yellow circle defines the area where I decided to aim my balloon. The terrain is mostly fields and it is relatively flat with an occasional hill that could by used as an observatory.

To project the predicted trajectory, I used CUSF Landing Predictor. It is a brilliant tool that can show you predictions based on your expected burst altitude and the ascent and descent rates up to 7-8 days ahead. But remember that the wind predictions evolve as the targeted day approaches and so does the trajectory. Above are two pictures demonstrating how predictions develop. The red dots with numbers show the landing sites and a number of days remaining to the actual launch. The green dot then shows the predicted landing site right at the time of the intended launch. The September 16 predictions show the development preceding my actual flight.

Naturally, I had questions about accuracy of the predictor. What helped me solve that was when one day I noticed XABEN77 high altitude balloon being released, so I immediately used the Landing Predictor to calculate the trajectory and then waited for the end of the actual flight. Above is the comparison. To me, it was sufficient and gave me an idea on how to think about the planning.

My method was to everyday use the Predictor to calculate trajectories with the same parameters for the maximum days possible. I knew I wanted to launch the balloon in the morning, so I filled 9AM as the time of the launch. This series of data gave me an idea on how to expect days complying with my demands. And also, there is usually a window of suitable days, so you can always move the launch one day back or forth.

The expectations I had about the flight and thus the values I used in the predictor were as follows. Based on the calculations I did in my excel spreadsheet and various online calculators, I used a value of 3.48m/s for the ascent rate and a value of 31434m as the expected burst altitude. As the descent rate, I used a rather overvalued figure of 5m/s. That, as I explained in the previous articles, was due to my expectation of something going wrong with the parachute. Anyway, in the actual launch day prediction, I used more values for four different predictions to obtain a range of possibilities. The combinations were 3.48/31434/5, 3.48/31434/10, 3.48/34434/5 and 3.48/34434/10. The reason for these values was to get an idea of what would happen if the balloon ascended to a higher altitude and thus spent more time in the easterly winds and what would happen if something went really wrong with the parachute.

The problem with my desired westward direction of the wind is that the winds usually head towards the east. I have noticed that there are 3 layers of winds that the balloon goes through on its way to 30km. The first layer starts at ground and reaches to more or less 13km. These are the winds I wanted to head west. The second layer stretches roughly from 13 to 25km. These winds change their direction as well. Above this layer remains the last one. Here, the winds head always to the east. If you desire your landing site to be close to your launch site, you should wait for such conditions that the winds in the three layers go against each other. In my case, the winds in the bottom layer headed straight west. In the middle layer, the direction was to the south. And as I mentioned, the topmost layer took the balloon east. In the picture above, the shifts in wind direction occur at 13253m and 26418m during the ascent, and at 24831m and 13176m during descent.

One more thing that came across my mind was the air traffic crossing the path of my balloon. I wanted to have some idea about the possibility of a collision, so I collected some data. In the picture above, I used the FlightRadar24's playback to mark every emerging plane's trajectory during a 6 hour period. Additionally, there is an airport about 30km from the launch site, and I know that the planes heading there or from there fly over my town in roughly 2-3km. There are usually 2-3 flights during a morning. The next think I did was to calculate the time durations the balloon would spend within the planes' expected altitudes. That gave me an idea about the situation. Baring in mind the dimensions of the planes and the balloon, the enormous extent of the 3 dimensional space the aircraft would move in and the fragility of the balloon set, I considered the possibility of a serious collision closing in on impossible.

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